Recently, capillary gel electrophoresis has been employed in order to analyze trace amounts of substances in organisms. The capillaries employed in such a method utilize narrow tubes having inner diameters of about 100 μm. Thus, trace amounts of samples are sufficient for use, and samples can be easily isolated. Members that are used for the capillaries include plastics that are excellent in their transparency, such as those represented by glass or polymethyl methacrylate. Use of capillaries having a hollow portion impregnated with a gel such as acrylamide as a member for a DNA chip that can collectively analyze genes has been attempted (WO 00/53736).
In order to analyze organism-associated substances such as DNA by capillary gel electrophoresis or using DNA chips, gel must be firmly retained inside a capillary.
When the volume of gel filling the hollow portion is reduced, however, a gap is generated at the interface between the inner wall of a capillary and the gel. At the time of analysis, a substance first flows into the generated gap, and this disadvantageously leads to lowered accuracy in analysis. When a capillary is used as a member for a DNA chip, the DNA chip is constructed by, for example, bundling several capillaries and cross-sectioning the bundle. When gel does not sufficiently adhere to the inner wall of the capillary, it disadvantageously becomes detached from the capillary at the time of cross-sectioning. Further, gel becomes detached from the capillary during analysis such as hybridization.
Introduction of a hydrophilic group on the inner wall of the capillary has been proposed as an example of a technique for enhancing adhesion between the inner wall of the capillary and a gel (U.S. Pat. No. 5,015,350). This is, however, a technique for enhancing the adhesion between a gel and the capillary by coating the capillary for hydrophilization. Thus, the strength of the adhesion between a gel and the inner wall is not sufficient, so that gel cannot be retained as the number of times that the capillary is used increases.
In the case of a glass capillary, a method for enhancing the ability of a gel to adhere thereto by chemically modifying the inner wall thereof with polyacrylamide has been developed (S. F. Y. Li et al., Capillary Electrophoresis, 173, 1992). This is, however, a technique for processing a glass surface with a bifunctional coupling agent that reacts with a silanol group on the glass surface. Accordingly, the effect of this technique cannot be attained by non-glass capillaries.
There has been a proposed method in which the shaping of a polymer capillary is conducted simultaneously with gel impregnation of the hollow portion of the capillary, thereby obtaining a polymer capillary having its hollow portion impregnated with a gel (JP Patent Publication (Kokai) No. 11-211694 A (1999)). With this technique, however, a gap is generated at the interface between the inner wall of the capillary and a gel when the volume of the gel is reduced during the shaping of the capillary.
Meanwhile, an attempt has been made in which hollow portions of porous hollow fibers are filled with water-insoluble polymers for the purpose of imparting functions such as hygroscopic properties and antistatic properties (JP Patent Publication (Kokai) No. 8-188967 A (1996)). This is, however, a technique for imparting new functions to fibers, which is unrelated to the adhesiveness of the gel filling the hollow portion.
More specifically, no conventional means had existed in the past that would sufficiently overcome the problem of the gap generated at the interface between the inner wall of the capillary and the gel when the volume of the gel is reduced or the problem of the gel becoming detached from the capillary when a DNA chip is constructed. Thus, it has been difficult to utilize a capillary impregnated with a gel for capillary gel electrophoresis or as a member for a DNA chip.